removals: all unicode encoding / decoding

Removed here includes:

* convert_unicode parameters
* encoding create_engine() parameter
* description encoding support
* "non-unicode fallback" modes under Python 2
* String symbols regarding Python 2 non-unicode fallbacks
* any concept of DBAPIs that don't accept unicode
  statements, unicode bound parameters, or that return bytes
  for strings anywhere except an explicit Binary / BLOB
  type
* unicode processors in Python / C

Risk factors:

* Whether all DBAPIs do in fact return Unicode objects for
  all entries in cursor.description now
* There was logic for mysql-connector trying to determine
  description encoding.   A quick test shows Unicode coming
  back but it's not clear if there are still edge cases where
  they return bytes.  if so, these are bugs in that driver,
  and at most we would only work around it in the mysql-connector
  DBAPI itself (but we won't do that either).
* It seems like Oracle 8 was not expecting unicode bound parameters.
  I'm assuming this was all Python 2 stuff and does not apply
  for modern cx_Oracle under Python 3.
* third party dialects relying upon built in unicode encoding/decoding
  but it's hard to imagine any non-SQLAlchemy database driver not
  dealing exclusively in Python unicode strings in Python 3

Change-Id: I97d762ef6d4dd836487b714d57d8136d0310f28a
References: #7257

1 files changed, 7 insertions, 21 deletions

diff --git a/lib/sqlalchemy/dialects/oracle/base.py b/lib/sqlalchemy/dialects/oracle/base.py
index 5a43205df..229a54b95 100644
--- a/lib/sqlalchemy/dialects/oracle/base.py
+++ b/lib/sqlalchemy/dialects/oracle/base.py
@@ -10,7 +10,7 @@ r"""
     :name: Oracle
     :full_support: 11.2, 18c
     :normal_support: 11+
-    :best_effort: 8+
+    :best_effort: 9+
 
 
 Auto Increment Behavior
@@ -341,6 +341,9 @@ and specify "passive_updates=False" on each relationship().
 Oracle 8 Compatibility
 ----------------------
 
+.. warning:: The status of Oracle 8 compatibility is not known for SQLAlchemy
+   2.0.
+
 When Oracle 8 is detected, the dialect internally configures itself to the
 following behaviors:
 
@@ -349,16 +352,12 @@ following behaviors:
   makes use of Oracle's (+) operator.
 
 * the NVARCHAR2 and NCLOB datatypes are no longer generated as DDL when
-  the :class:`~sqlalchemy.types.Unicode` is used - VARCHAR2 and CLOB are
-  issued instead.   This because these types don't seem to work correctly on
-  Oracle 8 even though they are available.  The
-  :class:`~sqlalchemy.types.NVARCHAR` and
+  the :class:`~sqlalchemy.types.Unicode` is used - VARCHAR2 and CLOB are issued
+  instead. This because these types don't seem to work correctly on Oracle 8
+  even though they are available. The :class:`~sqlalchemy.types.NVARCHAR` and
   :class:`~sqlalchemy.dialects.oracle.NCLOB` types will always generate
   NVARCHAR2 and NCLOB.
 
-* the "native unicode" mode is disabled when using cx_oracle, i.e. SQLAlchemy
-  encodes all Python unicode objects to "string" before passing in as bind
-  parameters.
 
 Synonym/DBLINK Reflection
 -------------------------
@@ -1439,8 +1438,6 @@ class OracleDialect(default.DefaultDialect):
     name = "oracle"
     supports_statement_cache = True
     supports_alter = True
-    supports_unicode_statements = False
-    supports_unicode_binds = False
     max_identifier_length = 128
 
     supports_simple_order_by_label = False
@@ -1576,17 +1573,6 @@ class OracleDialect(default.DefaultDialect):
             # use the default
             return None
 
-    def _check_unicode_returns(self, connection):
-        additional_tests = [
-            expression.cast(
-                expression.literal_column("'test nvarchar2 returns'"),
-                sqltypes.NVARCHAR(60),
-            )
-        ]
-        return super(OracleDialect, self)._check_unicode_returns(
-            connection, additional_tests
-        )
-
     _isolation_lookup = ["READ COMMITTED", "SERIALIZABLE"]
 
     def get_isolation_level(self, connection):